Auto merge of #6887 - xFrednet:4310-internal-metadata-extraction-lint, r=xFrednet

A metadata collection monster

This PR introduces a metadata collection lint as discussed in #4310. It currently collects:
* The lint ID
* The lint declaration file and location (for #1303)
* The lint group
* The documentation
* The applicability (if resolvable)
* If the suggestion is a multi-part-suggestion

This data has a slightly different structure than the current [lints.json](https://github.com/rust-lang/rust-clippy/blob/gh-pages/master/lints.json) and doesn't include depreciated lints yet. I plan to adapt the website to the new format and include depreciated lints in a follow-up PR :). The current collected json looks like this: [metadata_collection.json](https://gist.github.com/xFrednet/6b9e2c3f725f476ba88db9563f67e119)

The entire implementation is guarded behind the `metadata-collector-lint` feature and the `ENABLE_METADATA_COLLECTION` environment value to prevent default collection. You can test the implementation via:
```sh
$ ENABLE_METADATA_COLLECTION=1 cargo test --test dogfood --all-features
```

changelog: none

---

The size of this PR sadly also grew into a small monster, sorry! I definitely plan to improve on this! And it's totally okay if you take your time with this :)

r? `@phansch`
cc: `@flip1995`

Author: bors

.gitignore

@@ -29,6 +29,7 @@ out
 
 # gh pages docs
 util/gh-pages/lints.json
+**/metadata_collection.json
 
 # rustfmt backups
 *.rs.bk

Cargo.toml

@@ -52,6 +52,7 @@ rustc_tools_util = { version = "0.2.0", path = "rustc_tools_util" }
 deny-warnings = []
 integration = ["tempfile"]
 internal-lints = ["clippy_lints/internal-lints"]
+metadata-collector-lint = ["internal-lints", "clippy_lints/metadata-collector-lint"]
 
 [package.metadata.rust-analyzer]
 # This package uses #[feature(rustc_private)]

clippy_lints/Cargo.toml

@@ -20,6 +20,7 @@ pulldown-cmark = { version = "0.8", default-features = false }
 quine-mc_cluskey = "0.2.2"
 regex-syntax = "0.6"
 serde = { version = "1.0", features = ["derive"] }
+serde_json = { version = "1.0", optional = true }
 toml = "0.5.3"
 unicode-normalization = "0.1"
 semver = "0.11"
@@ -32,6 +33,7 @@ url = { version = "2.1.0", features = ["serde"] }
 deny-warnings = []
 # build clippy with internal lints enabled, off by default
 internal-lints = ["clippy_utils/internal-lints"]
+metadata-collector-lint = ["serde_json", "clippy_utils/metadata-collector-lint"]
 
 [package.metadata.rust-analyzer]
 # This crate uses #[feature(rustc_private)]

clippy_lints/src/lib.rs

@@ -1004,6 +1004,13 @@ pub fn register_plugins(store: &mut rustc_lint::LintStore, sess: &Session, conf:
         store.register_late_pass(|| box utils::internal_lints::MatchTypeOnDiagItem);
         store.register_late_pass(|| box utils::internal_lints::OuterExpnDataPass);
     }
+    #[cfg(feature = "metadata-collector-lint")]
+    {
+        if std::env::var("ENABLE_METADATA_COLLECTION").eq(&Ok("1".to_string())) {
+            store.register_late_pass(|| box utils::internal_lints::metadata_collector::MetadataCollector::default());
+        }
+    }
+
     store.register_late_pass(|| box utils::author::Author);
     store.register_late_pass(|| box await_holding_invalid::AwaitHolding);
     store.register_late_pass(|| box serde_api::SerdeApi);

clippy_lints/src/slow_vector_initialization.rs

@@ -7,7 +7,7 @@ use rustc_ast::ast::LitKind;
 use rustc_errors::Applicability;
 use rustc_hir::intravisit::{walk_block, walk_expr, walk_stmt, NestedVisitorMap, Visitor};
 use rustc_hir::{BindingAnnotation, Block, Expr, ExprKind, HirId, PatKind, QPath, Stmt, StmtKind};
-use rustc_lint::{LateContext, LateLintPass, Lint};
+use rustc_lint::{LateContext, LateLintPass};
 use rustc_middle::hir::map::Map;
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::symbol::sym;
@@ -157,26 +157,16 @@ impl SlowVectorInit {
         vec_alloc: &VecAllocation<'_>,
     ) {
         match initialization {
-            InitializationType::Extend(e) | InitializationType::Resize(e) => Self::emit_lint(
-                cx,
-                e,
-                vec_alloc,
-                "slow zero-filling initialization",
-                SLOW_VECTOR_INITIALIZATION,
-            ),
+            InitializationType::Extend(e) | InitializationType::Resize(e) => {
+                Self::emit_lint(cx, e, vec_alloc, "slow zero-filling initialization")
+            },
         };
     }
 
-    fn emit_lint<'tcx>(
-        cx: &LateContext<'tcx>,
-        slow_fill: &Expr<'_>,
-        vec_alloc: &VecAllocation<'_>,
-        msg: &str,
-        lint: &'static Lint,
-    ) {
+    fn emit_lint<'tcx>(cx: &LateContext<'tcx>, slow_fill: &Expr<'_>, vec_alloc: &VecAllocation<'_>, msg: &str) {
         let len_expr = Sugg::hir(cx, vec_alloc.len_expr, "len");
 
-        span_lint_and_then(cx, lint, slow_fill.span, msg, |diag| {
+        span_lint_and_then(cx, SLOW_VECTOR_INITIALIZATION, slow_fill.span, msg, |diag| {
             diag.span_suggestion(
                 vec_alloc.allocation_expr.span,
                 "consider replace allocation with",

clippy_lints/src/utils/internal_lints.rs

@@ -32,6 +32,9 @@ use rustc_typeck::hir_ty_to_ty;
 
 use std::borrow::{Borrow, Cow};
 
+#[cfg(feature = "metadata-collector-lint")]
+pub mod metadata_collector;
+
 declare_clippy_lint! {
     /// **What it does:** Checks for various things we like to keep tidy in clippy.
     ///